The present invention relates generally to operations performed in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides apparatus and methods for forming wellbore junctions.
Wellbore junctions are formed when a second wellbore is drilled intersecting a first wellbore. In a typical drilling program, the first wellbore may be designated a "parent" or "main" wellbore, and the second wellbore may be designated a "lateral" or "branch" wellbore. Depending upon the type of well, the type of formation surrounding the wellbore junction, etc., it is usually important for the completed wellbore junction to provide access to the parent wellbore above and below the junction, and to provide access to the lateral wellbore, and for the wellbore junction to prevent migration of fluids between formations intersected by the wellbores. It is also important for the casing, liners, or other conduits installed at or through the junction to be isolated from fluid communication with the formation surrounding the junction.
Of course, it is additionally important for the wellbore junction formation operation to be convenient and efficient, in order to save valuable rig time, and for the resulting junction to be reliable and long-lasting. Unfortunately, most prior methods of forming wellbore junctions have required time-consuming milling operations, in which openings are formed laterally through casing positioned in the parent wellbores at the junctions. The openings are formed so that cutting tools, such as drill bits, reamers, etc., may be passed through the openings in order to drill lateral wellbores extending outwardly from the parent wellbores. It would, therefore, be highly advantageous to provide apparatus and methods of forming a wellbore junction which do not require cutting through a casing sidewall downhole prior to drilling a lateral wellbore.
It is accordingly an object of the present invention to provide such apparatus and methods. Other objects and advantages of the present invention are set forth below.